Abstract 087: NPFF Receptors NPFF-R1 and NPFF-R2 in the Kidney: A Target for the Negative Control of Sodium Transport and Blood Pressure

Abstract

The kidney is critical in the overall regulation of fluid, electrolyte balance and blood pressure (BP). The renal dopaminergic system inhibits sodium transport in almost all nephron segments and is responsible for ≥50% of renal sodium excretion under moderate sodium excess conditions and is considered anti-hypertensive. Neuropeptide FF (NPFF), a morphine-modulating peptide, regulates food consumption and cardiovascular function through its interaction with two receptors, NPFFR1 and NPFFR2. NPFFR2 is anti-hypertensive under “normal” salt intake but becomes pro-hypertensive when salt intake is “high”. The ultimate phenotype depends upon protein/protein interaction. Hence, we tested NPFFR2 and dopamine receptor interaction in vitro using renal proximal tubule cells (RPTCs) and blood pressure in vivo in C57Bl/6J mice. NPFF is synthesized in RPT where NPFFR2 is expressed and co-localize with D 1 R. In RPTCs (n= 3-4/group), the D 1 R/D 5 R agonist fenoldopam (1 μM/30 min), increased cAMP production (4.23±0.56 pmol/mg/min vs . 2.54±0.19, vehicle; P<0.05) but was abrogated by co-treatment with NPFF (1 μM/30 (2.36±0.29 pmol/mg/min). Low NPFF (10 -10 and 10 -9 M) concentrations increased while higher concentrations had no effect (10 -8 and 10 -7 M), and slightly decreased (10 -6 M) cAMP production in RPTCs. Fenoldopam (1 μM/30 min) added to the basolateral side of polarized RPTCs grown in Transwells, increased intracellular Na + (117±4% versus the vehicle-treated control), indicating inhibition of basolateral Na + transport. This effect was prevented by co-treatment with NPFF (98±5%). Basolateral NPFF treatment alone decreased the intracellular Na + (-86.10±4.6%), indicating increased basolateral Na + transport and that renal NPFF may be a negative regulator of dopamine. In C57Bl/6J mice on 0.9% NaCl diet , renal-selective silencing of Npffr2 increased BP (115±3 vs 102±1 mmHg; P<0.05; n=3-5/group). By contrast, on 4% NaCl diet, renal-selective silencing of Npffr2 decreased BP (98±4 vs 113±3 mmHg; P<0.05; n=3-5/group), indicating that Npffr2 is antihypertensive on normal NaCl diet but pro-hypertensive on high NaCl diet. These contrasting effects may be due to D 1 R/D 5 R negative regulation of Npffr2 on normal salt diet which is lost when NaCl intake is increased.